This application claims the benefit of Korean Patent Application No. 1998-38159, filed on Sep. 16, 1998, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to to an X-ray image detecting device and, more particularly, to a thin film transistor (TFT) type X-ray image detecting device and a method for manufacturing the same.
2. Discussion of the Related Art
FIGS. 1 and 2 show a conventional TFT type image detecting device, which is disclosed in U.S. Pat. No. 5,498,880.
As shown in the drawings, arranged on a substrate 1 is a TFT 3 coupled to a storage capacitor 10 that is used for collecting charges. When the TFT 3 is switched by a scanning integrated circuit 4, charges stored in the storage capacitor 10 are directed to an integrated circuit 5.
An optical conductive layer 2 is deposited on the substrate 1 while covering all of the elements formed on the substrate 1. The optical conductive layer 2 is designed to form electron-hole pairs 6 (electric signals) in proportion to an intensity of an external signal such as an electric or magnetic wave. The optical conductive layer 2 functions as a converter for converting X-ray optical signals into electric signals. When charges formed by X-ray light are applied to a conductive electrode 7, a voltage Ev applied to the conductive electrode 7 causes the charges to be collected on a sensing electrode 8 formed under the optical conductive layer 2, and then stored in the storage capacitor 10.
In addition, when a voltage is applied to the TFTs 3 coupled to an M-number of gate wires, the charges stored in the storage capacitor 10 are directed to an external image system through an N-number of data wires. That is, the scanning integrated circuit 4 applies a voltage to the M-number of gate wires to turn On the TFTs 3, and the data integrated circuit 5 applies a voltage to the N-number of data wires to transmit the charges stored in the storage capacitor 10 to the external image system (see FIG. 2).
In the above described device, when the intensity of the X-ray light is low, it is very difficult to convert the X-ray light into charges. This problem can be overcome by reducing the trap density for trapping the charges within the optical conductive layer 2 and applying a large amount of vertical voltage (above 10V/xcexcm) between the conductive electrode 7 and the sensing electrode 8 to reduce the current generated by voltages other than the vertical voltage.
In addition, the charges generated on the optical conductive layer 2 by the X-ray light are also collected on a protecting layer 9 formed to protect a channel area 65 of the TFT 3. The charges collected on the protecting layer 9 are further directed to the channel area 65, making it difficult for the TFT to perform its switching-operation by generating leakage current even when the TFT is in an Off state. Furthermore, the leakage current causes the electric charges stored in the storage capacitor 10 to flow externally, making it impossible to display a desired image.
In addition, since the device has a xe2x80x9cmushroom structurexe2x80x9d in which the TFT 3 and the storage capacitor 10 are covered by the protecting layer 8, the electric potential is increased as the charges are collected in the storage capacitor 10. The increased electric potential causes the amount of a parasitic capacitance formed between the protecting layer 8 and the TFT 3 to be increased. The amount of the parasitic capacitance can be reduced by increasing the thickness of the protecting layer 8. However, if the thickness of the protecting layer 8 is increased, since a large amount of the charges are induced into the channel area 65, the leakage current is increased even when the TFT is in an Off state. By forming an organic insulating layer having a thickness of more than 2 xcexcm on the storage capacitor 10, the amount of the parasitic capacitance also can be reduced. However, an additional time-consuming process for depositing the organic insulating layer is required, increasing manufacturing costs.
Accordingly, the present invention is directed to thin film transistor type X-ray image detecting device and method for fabricating the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a TFT type X-ray image detecting device with an improved switching operation by reducing a leakage current, thereby providing a clear image.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention provides a method for fabricating an X-ray image detecting device, the method comprising: forming a gate element on a substrate; forming a gate insulating layer on the substrate while covering the gate element; forming an ohmic contact layer on a portion of the gate insulating layer corresponding to the gate element; forming source and drain electrodes on the ohmic contact layer simultaneously with forming a first common electrode on the gate insulating layer; forming a storage capacitor insulating layer on the source and drain electrodes and the first common electrode; forming first and second contact holes on a first portion of the storage capacitor insulating layer corresponding to the drain electrode and a second portion of the storage capacitor layer the first common electrode, respectively; and forming a sensing electrode and a second common electrode on the storage capacitor layer such that the sensing electrode and second common electrode contact the drain electrode and the first common electrode through the first and second contact holes, respectively.
The method may further comprise forming an optical conductive layer on the sensing electrode and second common electrode; and forming a conductive electrode on the optical conductive layer.
Preferably, forming the ohmic contact layer further comprises: forming a pure amorphous silicon semiconductor layer on the gate element; and forming an impurity-containing silicon semiconductor layer on the pure amorphous silicon semiconductor layer. The first and second common electrodes are grounded. The storage capacitor insulating layer may be made of an organic material or an inorganic material. Preferably, the inorganic material comprises a silicon nitride. Preferably, the optical conductive layer is made of an amorphous compound.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.